1. Field of the Invention
This invention relates to a method of, and apparatus for, remotely testing a communications line, and more particularly to a method of, and apparatus for, testing a communications line to ascertain its suitability, under high frequency transmissions, for transmitting data at high bit rates.
2. Description of Related Art
There is a need to conduct tests and perform measurements on a communications line, including a telephone line, such as the characteristics of line loss, noise and resistance. This is so that the line's suitability for high frequency digital systems like pair gain, basic rate ISDN and Internet connections can be established. Generally, at high frequencies, the loss in signal magnitude is much higher than at low frequencies. For example, at 100 kHz, the line loss can be as much as 45 dB for a small pair gain system. This is primarily due to the increase in inductance on the line as frequency increases. A Plain Ordinary Telephone Service (POTS) line can often tolerate adverse transmission conditions caused by bridged taps, split pairs, poor joints and low insulation resistance. However, these conditions seriously affect the operation of high frequency digital systems and therefore must be identified.
Previously there has been no known method of measuring line loss and for performing all other necessary measurements remotely from the receiving end of a communications line. One arrangement has consisted in setting up identical measuring instruments one at each end of the line under test. Each instrument is very expensive and furthermore, switching of the instruments between different functions to be measured has to be performed manually. There is also known Australian Patent No. 604878, in the name of the applicant, which discloses a system for remotely disconnecting and short-circuiting a pair of conductors. However, the system disclosed therein does not facilitate remotely switching between a plurality of measurement functions such that the required circuit elements to enable such measurement are connected to the communications line at both ends of the line, that is, the sender end and the receiver end. The disclosed system only permits sequential switching between functions and does not allow for random switching from one function to another in order to connect circuitry across a communications line to enable a characteristic to be measured and/or tested.